I want to build a two-way using the HiVi B3n in an open baffle with a Focal 6M115 6.5 in a MLTL. I'm having trouble designing the baffle geometry for the B3N. I purchased rights to MJK's MathCad models, but all of his models are two-way designs. I was thinking I would cross them at around 500hz. Can someone help a brotha out?

MJK's MathCad models assume that you aren't mix and matching enclosure types. You can run the OB model with a B3N and manually splice to the results you get with the Focal in the MLTL. Unfortunately this won't help you see how the drivers integrate together in the crossover region.